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Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Mayfly Species Diphetor hageni (Little Blue-Winged Olive)

This is one of the most important species of the Baetidae family. It is distributed across the country but most of its fame comes from excellent hatches in the West. Prior to many other former species being combined with Baetis tricaudatus, most angling literature considered it the most populous and widespread western species of the Baetidae family.

Taxonomic History

This species was previously known and mentioned in the angling literature as Baetis parvus in the West and Baetis devinctus in the East.

Where & when

Time of year : April and May, then another brood in September and October; sometimes another intermediate brood

Preferred waters: Fertile streams

Hatching behavior

The nymphs and duns are both important during this hatch.

Spinner behavior

Fred Arbona in Mayflies, the Angler, and the Trout describes peculiar spinner behavior in this species:

Spinners gather in the mornings or evenings, and their tight swarms can be observed over the banks of the stream. After mating, the spinners suddenly vanish and reappear spent on the water.

Nymph biology

These nymphs are very versatile: cold or warm water, slow or fast water, spring creeks and freestone streams.


Dorsal abdominal markings on the nymphs used to differentiate the species in these older publications have since proved unreliable. The easiest way to tell them apart from B. tricaudatus is their lack of gills on the first abdominal segment. Telling adults apart is equally tough. Duns of D. hageni are typically a little smaller, but their bodies can also be olive, brownish olive and even two toned with thoraxes a shade of brown or tan with paler olivacious abdomens.

Specimens of the Mayfly Species Diphetor hageni

1 Nymph

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